1. Field of the Invention
The present invention relates to a control apparatus for a vehicular drive system including an electric differential portion and a mechanical power transmitting portion which are disposed in series with each other in a power transmitting path between an engine and a drive wheel of a vehicle, and more particularly to techniques for limiting rotating speeds of input members of the mechanical power transmitting portion in the event of a failure of a coupling device of the mechanical power transmitting portion during running of the vehicle, and for thereby assuring high durability of those input members.
2. Discussion of Prior Art
There is known a vehicular drive system including an electric differential portion and a mechanical power transmitting portion which are disposed in series with each other in a power transmitting path arranged to transmit an output of an engine to a drive wheel of the vehicle. JP-2005-264762A discloses an example of such a drive system for a hybrid vehicle. This vehicular drive system includes a power transmitting member for transmitting a vehicle drive force from an engine to the mechanical power transmitting portion through the electric differential portion, and a second electric motor disposed in a power transmitting path between the power transmitting member and the drive wheel. The mechanical power transmitting portion is a step-variable automatic transmission mechanism which is arranged to change the rotating speed of its input rotary member in steps while the vehicle drive force is received by the input rotary member from the engine through the power transmitting member.
The vehicular drive system as disclosed in the above-identified publication uses the mechanical power transmitting portion provided with a coupling device such as an input clutch, through which the vehicle drive force received from the electric differential portion is transmitted to the drive wheel from the mechanical power transmitting portion.
When a torque capacity of the coupling device such as the input clutch is reduced in the event of a failure of the coupling device or any component provided to control the coupling device during running of the vehicle at a comparatively high speed, there is a possibility that an input rotary member of the mechanical power transmitting portion disposed on one side of the coupling device that is nearer to the engine is rotated at an excessively high speed.